Rectification of mixed gases



Aug. 11, 1953 J. A. HUFNAGEL RECTIFICATION OF MIXED GASES 2 Sheets-Sheetl 1 Filed March 50, 1948 HTTORNEY Aug. 11, 1953 Filed March 50. 1948 J. A. HUFNAGEL RECTIFICATION OF MIXED GASES l.2 Sheets-Sheet 2 fa/m Y INVENTOR.

/TTOR/VEY Patented Aug. 1.1, 195,3

UNITED :STATES PATENT OFFICE vRECTIFICATION F MIXED GASES John A.'-'Hufna;gel,-1V.Iineola;z N. Y'.-,-assignor to Y Hydrocarbon Research,Inc.;New York, N. Y.,

a corporation of ANew Jersey Application -March 30, 1948; Serial N o.' 17,998

13- Claims.

This invention relates to. the-productiony of 'oxygen by. the liquefaction and-irectication of All temperaturesherein are in degrees E. and pressures in pounds per square inch gauge.

Oxygen is commonlyproduced by Aliquefaction of air and rectication at Y'low:temperaturesif:The refrigeration necessary for`A liquefaction is supplied to the air after it has been compressed .and water-cooled to approximately room temperature by indirect heat exchange with the-'lefiluent products of rectification. @ne of the morewrecent methods of producing oxygeninvolvesowing the incoming air through a v reversing :exchanger through which flows a `rectification productsuoh as nitrogen or oxygen, the airrecovering/.the-cold content of the rectification product and-being thus cooled to a temperature closefto `its liquefaction point at the pressure exstinginwthe heat exchange zone, thereby substantially completely removing all carbon dioxidev present inzrthexair. A minor portion of the thus cooled .air'stream is thereafter warmed by heat exchangefwthfone of the warmer streams of fluid media flowing in the system, preferably by passage :through's'the aforesaidheat exchange zone, to aztemperature such that upon subsequent expansion littlefor no condensation or formation of vliquid airwin :the expander takes place. .The thus 4-warmed minor portion is expandedto produce the refrigeration necessary to compensate for cold losses resulting from the difference kin enthalpybetweeni- .the incoming air and the .outgoing Vproducts ofirectiiication and for heatleaks intonthefs'ystemrrand the expanded air is introduced intoytheirecticae tion system where it is rectified tosrecover'the oxygen content thereof. The remainingmajor portion of the air is also introduced;. intoxthe rectication system where it, is .recti'ed aThe iow of air and that of the recticationtproduct are periodically reversed inthe reversingwheat exchanger, so that uponA each otthefreversals the rectification product substantially completely removes the carbon dioxidexand'other condensibles deposited in the reversingr exchangerfduring the preceding step of the process.' Such reversal may take place about'every three minutes.;l It has also been proposed torecycle. through# at least the -cold end of the reversingtexchanger nitrogen, oxygen, or an extraneousgastdfacilif-vr tate purging of the exchanger.

In operation, it has beenA found that.. thetemperatures oi the gaseous streams.leavingrreversing exchangers ii-uctuate.A within -.:wde.f:1imits, sometimes as much aslOl' or more, Such- 2 :fluctuations cause considerabledisturbance in the lwoperation ofthel oxygen plant and impair its eil'ciencyfr-For instance, fluctuations in the temperature of the air flowing to the expander interferes with .its best performance. Likewise,y these temperature variations may lead tc the formation f fof liquid-air within the reversing exchangersidur- 4ingcertain portions of the reversal cycles with .f-consequent' loss of air during the subsequent 0 ',-cy-clesffwhen a l.rectification product stream is -w'lusecltopurge thereversing exchangers of con- .'stituentsdeposited therein by the air. These temperature .variations also deleteriously. affect .the `operation of the rectification system.

lH'Ihe-cauSesOf Vtemperature,fluctuations in the ngaseousstreams leaving reversing exchangers are manifold. In .recuperative-type reversing eX- ;=changers,theprincipal cause of temperature '..tfluctuationsk is .the asymmetrical arrangement yof 205,1;hgiiowA paths in the exchanger; typically, a f.:,recuperativeyreversing.exchanger will have three ow paths formed by three concentric pipes of i increasingdiameter, the smallest central pipe beingzused for ay recycle stream, the annulus be- 5..;tweene.the= smallest and intermediate pipes. and

the 'annulus between .the intermediate and largest 1: `pipesbeing=alternately used for the flow of air mand a frectication product. Thus, during 'one step ofbperationthe air flows through the path .adjacent .that of the recyclegas and during the .fnextrstep it ows through the path remotefrom that` of the .recycle gas. In a 4regenerative reversing exchanger, the principal cause voi temperature fluctuations `is-more obvious since during one step tofpoperation a coldstream of rectification product flows..therethrough tor chill its mass and during the next step a swarm stream of `air ows therethrough to vrecover .the stored refrigeration; imfrommthe .I start to the end Of each step of ythe operation it isclearxthatthe temperatureof the .'fregenerator'changes and these temperature -;changes-are naturallyreflected inthe temperatures ofthe gaseous streams issuing therefrom.

1 `It is an object of this invention to provide a 45, process of producing oxygen in which such temff-perature iiuctuationsA are materially reduced, de- ;-',sirablyto the point-Where variations in the-temperature of a gas stream entering the expander .-or rectification systemor reversingfexchanger is ofthe-orderof 1 F.

Another object is toprovide a novel arrange- ,.,ment of apparatus for practicing such process.

Otherobjects and advantages of this invention .-,will lbe2 apparent from the following` detailed descriptionthereof.

In accordance with this invention a gas stream of the oxygen process which tends to fluctuate in temperature, after leaving the reversing exchanger and before entering into a succeeding stage of the process, such as the expander, rectiiication system, or before being recycled through the reversing exchanger, is passed through a chamber containing a predetermined mass of high heat conducting material presenting a large heat transfer surface area and so designed that little pressure drop takes place in the gas stream passing therethrough. Such chamber functions as a damper to check or limit temperature fluctuations and is herein referred to as a damper chamber'. Once the steady state of operation is reached this damper chamber functions to bring the gas stream exiting therefrom to the desired temperature at which the gas should enter the succeeding stage of the process. Accordingly, if the gas stream entering this chamber is above this desired temperature, the gas stream gives up its excess heat to the chamber and leaves at a temperature substantially the same as or a little above the desired temperature, e. g., about 1 F. above this temperature. On the other hand, if the entering gas is at a temperature below this desired temperature, it is heated in its flow through this chamber and leaves at a temperature close to the desired temperature. The damper chamber in operation is accordingly heated or cooled as the entering gas stream flowing therethrough enters at a temperature above or below the desired temperature, the gas stream leaving this chamber at a temperature little above or below the desired temperature. Desirably the chamber contains a weight of high heat conducting material, preferably metal, over which the gas stream passes, of from 1% to 10% by Weight of that in the flow path of the reversing exchanger with which it is associated, preferably about of the weight of heat conducting material in such a flow path.

In the accompanying drawings forming a part of this specification and showing for purposes of exemplification preferred layouts of equipment for practicing the process of this invention,

Figure 1 illustrates diagrammatically a preferred layout of apparatus for practicing the process of this invention, which apparatus involves reversing exchangers in which the air and rectification products fiow in indirect heat exchange relation, i. e., reversing exchangers of the recuperative type;

Figure 2 illustrates a modified arrangement of apparatus for practicing the process of this invention in which the reversing exchangers are of the regenerative type; and

Figure 3 is a section through one form of damper chamber taken in a plane normal to the line of flow of gas therethrough.

It will be understood the drawings illustrate diagrammatically preferred apparatus for practicing this invention, but the invention may be carried out in other apparatus, for example, any desired number of reversing exchangers may be used in lieu of those shown in the drawings; each of the reversing exchangers may be replaced by two or more smaller exchangers placed in series and/or parallel, if desired, and other rectification systems may be used in lieu of that shown in the drawings.

Referring to Figure 1, I0 is a heat exchanger which may be of any well known type and which in the drawing is shown consisting of two sections II and I2. In the embodiment shown in the drawing, section II consists of a single shell in which are provided two flow paths, namely, interior path I3 and concentric path I4, disposed in heat exchange relation with each other. Section I2 consists of three paths I5, I6 and I1 disposed in concentric relationship in heat exchange relation with each other. Each section has in each of the paths suitable ns of heat conducting material, e. g., copper or aluminum, promoting rapid and efficient heat exchange between gaseous media flowing through the paths in heat exchange relation with each other. For purposes of illustration and in the interests of simplicity, each flow path in an exchanger is shown on the drawings as consisting of a single tube, the several paths being disposed concentrically. Actually, however, each path in each exchanger may comprise a multiplicity of tubes for flow therethrough. As the construction of the heat exchanger per se does not form a part of this invention, and as it may be of any well known type, it is believed further description thereof is unnecessary.

Paths I3 and I4 of exchanger section II are connected with paths I6 and I1 of exchanger section I2 by lines I8 and I9, respectively. Section I2 also contains flow path l5 for iiow of a minor portion of the cold air stream therethrough. This flow path leads into a line 20 which communicates with a damper chamber 2|. This chamber contains a predetermined mass of high heat conducting material, such as copper or aluminum, presenting a large heat transfer surface area and designed so that little pressure drop takes place in the gas stream passing therethrough. For example, damper chamber 2I comprises a housing 22 (Figure 3) having therein a plurality of longitudinally extending channels 23 produced by winding on a suitable support 24, a strip of aluminum having one side 25 flat and the other side 26 provided with closely spaced integral ribs 21 to produce a plurality of convolutions having the closely spaced ribs extending across the width of each convolution and forming the longitudinally extending channels 23 in the annular spaces between the convolutions, the ribs of one convolution contacting the flat surface of a contiguous convolution. Such strip may have an overall thickness of approximately .07 inch and the ribs may be spaced apart a distance of approximately .l5 inch from the center of one rib to the center of the next rib. Thus an exceptionally large mass of high heat conducting metal and high area of surface is provided per unit of volume of damper chamber. The type of packing hereinabove described is disclosed more fully and claimed in co-pending application Serial No. 19,952, filed April 9, i948, now Patent No. 2,602,645. Alternatively, the damper chamber 2l may be constructed and designed so that it is similar to the regenerators disclosed and claimed in co-pending application Serial No. 783,498, filed November l, i947, now Patent No. 2,585,912, or may be of any other suitable construction providing a mass of high heat conducting material presenting a large heat transfer surface area and so designed that little pressure drop takes place in the gas stream passing therethrough.

Paths I3, I6 and I4, I1 of regenerator sections II and I2 are the paths through which air and nitrogen iiow, the flow of these two media through their respective paths being periodically reversed so that during one step of the process air flows through paths I4, I1 and nitrogen through paths I6,'|3 anduponreversalfduring the succeeding step airiloWs' through paths' I3, I5 and nitrogen through paths' I1 andV I4. Y Reversal or now is accomplished bysuitably positioning reversing valves 29, 30 which may be of any well known type. Valve 29 is disposed in a pipe line system consisting of an air inlet pipe 3I, nitrogen exit pipe 32 leading to any suitable point of nitrogen disposal and pipe lines'. 33, 34 leading to one end of paths I3, I4. Lines 35,- 36 lead from paths I6, I1, respectively, to valve 30. Air exit line 31 leads from valve 30 and nitrogen inlet line 39 leads into this valve.

A second heat exchanger 39 is provided consisting of two sections 40, 4I, which exchanger in general is similar to heat exchanger' I0, except that it is approximately one-fourth the volumetric capacity of heat exchanger- I0. Section'li is provided with concentric ow paths 42,` 43 and section 4I with the concentric flow paths 44,45 and 46. Paths 42 and 45 are connected by a line 41 and paths 43 and 46 by a line 48. Oxygen and air periodically flow through paths 42, 43 of section 49 and paths 45, 46 of section 4I in heat exchange relation with each other and with a stream of nitrogen flowing through path 44 of section 4I. The iiow of air and oxygen through their respective paths is periodically reversed so that during one step of the process air flows through paths 43 and 46 and oxygen flows through paths 45 and 42. Upon reversal during the succeeding step, air flows through paths 42 and 45 and oxygen through paths 46 and 43. Reversal of ow is accomplished by suitably positioning the reversing valves 49 and 50 which may be of the same type as valves 29 and 39. Valve 99 communicates with the main air line through line 5i and is connected by lines 52 and 53 to one end of paths 42, 43. Valve 49 is provided with an oxygen exit line 54 leading to `a suitable oxygen storage tank or point of consumption. Valve 59 is connected to the cold end of paths 45, 4S by lines 55, 56, respectively. Air line 51 leads from valve 56 into a line 58 into which also leads the air line 31 from valve 30. Oxygen line 59 leads into valve 59.' Line 58 leads into a damper chamber 60 which may be of the same general construction as damper chamber 2l, except that it is of substantially larger capacity to accommodate the flow of air passing therethrough.

A line 6I leads from damper 60 into an air line 8l and a line 62 provided with a control valve 53. A branch line 64 leads from line 62 and is equipped with a control valve 65. A minor portion of the air flowing into line 62 iiows through branch line 64 into the ow path' I5 of exchanger section I2 in heat exchange relation with the air and nitrogen owing through the other two ow paths I6 and I1 in this exchanger section.

A line 61 leads from iioW path 44 through a damper chamber 66 which may be of the same general type as damper chambers 2I and 60 hereinabove described. A minor portion of nitrogen passed through flow path 44 ows throughv line 61 and damper chamber 66 into nitrogen line 38 which in turn leads into valve 30. It will be understood that, if desired, the minor nitrogen stream may be passed through flow path I5 in exchanger section I2 in heat exchange relation with the air and nitrogen streams flowing through the other two flow paths in this exchanger and the minor air stream passed through flow path 44 in yheat exchanger section 4I in heat exchange'relation with the airand oxygen passing through the metric. Y. capacity of lthe Q oxygen new paths. i i If desired/exchangers in which the oxygen l.and

' nitrogen now paths are of the same volumetric capacity may bey employed, in which case four air-nitrogen reversing exchangers are employed for each air-oxygen reversing exchanger.r Also,

' of the total -air cooled by indirect heat exchange with the oxygen and nitrogen products of rectiiication, about 20% flows through the air-oxygen reversing exchanger and about 80% through the air-nitrogen exchanger.

A line11 leads from the damper chamber-'2| into an expander 1I which may be a centrifugal expander or turbine of any Well knownv type. Line 62 communicates with this line. 1D. .Byfcontrol' -ofyalve-SE a *portion of theair-which isto be expanded, say about flows from line 62 into and through line. 64, path I5 where the air is warmed, imparting some of kits cold content to the air flowing in a countercurrent :direction through exchanger section I2. The thus warmed air leaves path I5 through line 29, passes .through damper chamber 2i and ows through line-10. By control of valve. 63 inliner 62,-the remaining portion of the air to be expanded, say about 65%,

' flows from line 62 into line 10 where it mixes with the warmed air owing through this line, the resulting air mixture thus being warmed to a temperature such that no condensationror formation of liquid air takes place in expander 1I with consequent improvement in the. efciency of the expander. The expanded air leaves expander 1I through a line 12 leading into the low pressure stage of a rectication system hereinafter described.

The rectification system 15 comprises two'columns 16 and 11. Column 16 is operated. at a pressure of from about60 to about 100 pounds, preferably atabout 70 to 85 pounds and column 11 at a pressure of from about 2 pounds to about 12 pounds, preferably at about 5 pounds. These columns, as customary, are provided with rectification plates of the bubble-capr or other desired type. Air is supplied to the base portion of the high pressure column 16 through a line 18 which passes through a non-reversing heat exchanger 19 and leads from a second nonreversing heat exchanger 80. The air line18I leads from air line 6I to this non-reversing heat exchanger 8D. Crude oxygen containing approximately 40% oxygen, the rest being chiefly nitrogen, flows from the base oi-column 16 through line 82 which passes through a non-reversing heat exchanger 83. Upon flow through the expansion valve 84 in line 82 the crude oxygen is flashed entering column 11 at 85. A line 86 leads from the top of column 15, passes through a nonreversing heat exchanger 81 into a vline `having one branch 38 for returning liquid reflux comprising chiefly nitrogen to column '16 and another branch SQ passing through a non-reversing exchanger 99 and leading into the'lowpressure column 11 at 9|. An expansion valve 92 is disposed in branch 89.

As hereinabove described, expanded air from expander 1| enters the low pressure column 11 through line 12. The base of this column is provided with a line 93 passing through the nonreversing heat exchanger 81, this line having a return portion 94 leading into the low pressure column 11 at 95. The lines 93 and 86 and the cooperating heat exchanger 81 function as a condenser-reboiler; liquid oxygen flows through line 93 through exchanger 81 in indirect heat exchange relation with the gaseous stream comprising chiefly nitrogen passing through line 8B which causes vaporization of the liquid oxygen to take place, the oxygen vapors flowing into column 11 at 95. Nitrogen line 95 leads from the top of column 11 to exchanger 99. A line 91 leads from exchanger 99 to exchanger 83. A line 98 leads from exchanger 83 to exchanger 19. A line 99 leads from exchanger 19 and is provided with branch |90 leading into flow path 44 0f exchanger section 4|. Flow through branch |00 is controlled by valve IOI. Branch line 38, flow through which is controlled b-y valve |92, leads from line 99 to reversing valve 30.

A valve controlled drain line |03 communicates with line 93 through which the body of liquid oxygen in the base of tower 11 may be drained, when desired.

In operation of the equipment of Figure 1, air from the main air line at a pressure of 60 to 100 pounds and a temperature of '10 to 110 F. is divided into two streams, one oi which flows through line 3|, valve 29, line 34, ow path I4, line I9, iiow path I1, leaving through line 3B and flowing through valve 30, line 31 into line 5B. The air stream is thus cooled in its flow through flow paths I4 and I1 to a temperature near its liquefaction point and all carbon dioxide and moisture, if any, removed therefrom and deposited in the iow paths I1 and I4 of exchanger sections I2 and II, respectively.

Nitrogen flows from the low pressure column 11 through line 96, into exchanger 90, line 91, exchanger 93, line 99, exchanger 19, line 99. From this line a minor portion of this nitrogen stream,

say about 10% by volume, flows through branch line |09, into and through now path 44 in exchanger section 4 I. The nitrogen is thus warmed by heat exchange with the air stream flowing through exchanger section 4 I, The thus warmed nitrogen stream exits through line 91 and flows through the damper chamber 55, which minimizes fluctuations in the temperature of this nitrogen stream. The nitrogen from chamber flows at a substantially constant desired temperature into branch line 3S where it mixes with the major portion of the nitrogen flowing through this branch line. The mixture at a substantially constant temperature, since the major portion of the nitrogen is at a substantially constant temperature, enters valve 30 and ows from this valve through line 35, fiow path I9, line I8, flow path I3, line 33 and valve 29, exiting through the nitrogen exit line 32.

Another air stream flows from the main air line through line I, valve 49, line 53 into and through flow path 43, line 49, into and through flow path 46, line 55, valve 59, line 51 into line 5S where it joins the air stream from line 31. Simultaneously, oxygen from the low pressure column ows through line 59, exchanger 80 into valve 50, line 55, flow path 45 Where the oxygen flows in heat exchange relation with the air and nitrogen flowing through paths 46 and 44, respectively. The oxygen from flow path 45 flows through line 41, flow path 42 in exchanger section 40, through line 52, valve 49 and thence into the oxygen exit line 54. The air is thus cooled to a temperature close to its liquefaction point in its flow through ow path 4S. This thus cooled air from line 58 flows as a unidirectional stream through damper chamber 60 over the large mass of high heat absorbing material therein, thereby minimizing temperature fluctuations and causing the cooled air to enter lines 8| and 62 through line 6I at a substantially constant temperature.

A minor portion of the air stream in line 62, e. g., about 20%, flows partly through line 54 into and through iiow path I5 Where it is warmed by heat exchange with the countercurrent air stream flowing through iiow path I1. This warm air stream flows through line 29 and damper chamber 2| which functions to minimize fluctuations in the temperature of the air stream entering line 10. The other part of the minor portion of the air stream from line 62 flows into line 10 where it mixes with the warm air flowing therethrough, the mixture entering xpander 1| at a substantially constant temperature such that substantially no liquid air is formed in the expander 1|. The expanded air from expander 1| flows through line 12 and enters the low pressure stage 11 of the rectiiicationsystem 15.

The remaining major portion of air, e. about of the air from line 6|, flows through line 0| into the non-reversing exchanger 80 where the air is further cooled by the oxygen flowing in indirect heat exchange relation therewith through line 59. From exchanger 89 the air iiows through exchanger 19 Where it is still further cooled by flowing in indirect heat exchange relation with the nitrogen passing through this exchanger, thc thus cooled air entering the high pressure column 16.

Upon reversal, as indicated by the dotted setting of reversing valves 29, 30, 49 and 50. which reversal may take place every three minutes, air iiows through line 3|, valve 29, line 33, flow path I3, line I3, flow path I0, line 35, valve 30, line 31 into line 58. Air also flows through line 5|, valve 49, line 52, flow path 42, line 41, flow path 45, line 55, valve 50, line 51 into line 58 where it mixes with the air stream iiowing into this line 50 from line 31. The air in its flow tharough the exchangers IG and 39 is cooled to a temperature close to its liquefaction point, this temperature, however, fluctuating depending upon the variables affecting the operation of the exchanger.

Simultaneously, a minor portion of the nitrogen flowing through line 99 passes through branch line |00 into and through flow path 44, line 61, damper chamber 66, into the nitrogen line 38 where it mixes with the nitrogen flowing through this line. The resultant mixed nitrogen stream passes through valve 30, line 36, flow path I1, line.|9, flow path I4, line 34, valve 29 into the nitrogen exit line 32. The product oxygen stream flows through line 59, valve 50, line 56, flow path 45, line 48, flow path 43, line 53, valve 49, exiting through oxygen line 54. The flow of the various streams into and from the expander, into, through and from the rectification system, are the same as hereinabove described.

It will be noted that flow through the ow paths 44 and I5 of exchanger sections 4| and I2, respectively, always takes place in the same direction throughout the operation of the process. Flow of the nitrogen and air through their respective ilow paths in exchanger I and the flow of the oxygen and air through their respective flow paths in exchanger 39 is periodically reversed. Flow of the gaseous streams through damper chambers 2| 60 and 66 always takes place in a unidirectional path over the mass of high heat conducting material therein, the temperature of the gas stream entering this path uctuating within relatively wide limits, say F. or even more, and the gas stream exiting with materially smaller temperature fluctuations, say only 1 or 2 F. Reduction in temperature fluctuations of the gas streams entering the expander, rectiiication system and reversing exchangers improves the operation of these units. For example, by having the nitrogen enter the flow path in section I2 at a controlled substantially constant temperature, it is possible to have the nitrogen enter at a temperature close to that of the exiting air stream so that throughout the operation there is a relatively small temperature differential between the temperature ofthe exiting air stream and of the entering nitrogen stream thereby7 improving the purging eiected by the nitrogen stream.

One example of the operation of the process of this invention in the apparatus shown in Figure l is described below. It will be understood this example is given for purposes of exemplication only and the invention is not limited thereto. The' example refers to an oxygen plant operating in a locality where the atmospheric pressure is 13.1 pounds per square inch absolute.

Air under pressure of 74.6 pounds and a temperature of 95 F. is supplied through lines 3l and 5l to valves 29 and 40, respectively. The air flows through the flow paths in the exchangers !6 and 39 and leaves these how paths at a temperature fluctuating within the range of 270 to 280 F.; the air then flows through damper chamber 60 leaving this chamber at a temperature of about 275 F., at which temperature it enters lines 8! and 62.

Approximately of the total air introduced into the process is expanded in expander'll. Of this air to be expanded, approximately 33% flows through line 6d into ilow path I5, entering this path at a temperature of 275 F. and being heated in its ilow through this path to a temperature within the range of from 195 to 205 F. The air stream then flows through damper chamber 2l, exiting from this damper chamber at a temperature of about 200 F. The remaining 67% of the air to be expanded at a temperature of 275 F. passes through line 52, mixing with the air stream flowing through line l0, producing a mixed air stream having a temperature of about 250 F., and a pressure of 72.9 pounds. This mixed air stream enters expander 'H and is expanded to a pressure of 6.4 pounds, its temperature being reduced to about 305 F., at which temperature and pressure it is introduced into low pressure column il'.

The remainder of the total air, approximately 80%, at a temperature of 275 F. ows through line E! into heat exchanger 8i) where it' passes in heat exchange relation with an oxygen stream at a temperature of 293 F., ilowing through line 59 from the low pressure column l?. The air is thus cooled to a temperature oi 276.5 and the oxygen stream warmed to a temperature of 253 at which temperature it enters one or the other oi the ilow paths 65, 46 in exchanger section lli. The air at a temperature .of

276.5 F; passes through the heat rexchanger 'I9 inheat exchange relation with the nitrogen stream flowing into this exchanger at a temperature of 293 F. and undergoes partial liquefaction (about 1.5% being liquefied) and passes at a temperature of -276.5 F. and a pressure of 72 pounds into the high pressure column 16. f The nitrogen ilowing through .heatv exchanger 'I9v is thus warmed to a temperature of 290.4 F.

yAbout 8.5% by volume of the nitrogen stream at a temperature of 290.4 F. ilows through line 00 and flow path lili, leaving this ow path at a temperature of from to 205 F., at Vwhich temperature it ows lthrough line 61 and damper chamber 60, leaving this damper cham- Jer at a temperature of about 200 F., at which temperature it mixes with the remaining major portion of the nitrogen stream owing through line 38. The resulting nitrogen streamhas a temperature of about 283 at which temperature it enters exchanger section |2.. The nitrogen leaves exchanger section Il. at a temperature of 82.7 F. and under substantially atmospheric pressure.

Oxygen at a temperature of 293 Rand a pressure of 6.6 pounds flows through heat exchanger 86 where, as above described'its temperature is elevated to 283 F., `at which` temperature it enters exchanger section 4|, and leaves exchanger section 40 at a temperaturel of 02.7 F. and at substantially atmospheric pressure.

In the operation of the rectication system-15, crude oxygen at a temperature oi 280 F. and a pressure of .72 pou-nds passes through line -82, and heat exchanger 83, in indirect heat eX- change relation with nitrogen flowing into this exchanger.v The crude oxygen is thus cooled to a temperature of 287.6 F. and is then flashed in its-iiow through expansion valve 84, entering column il' as a vapor-liquid mixture at a temh perature of 302.5 F. and a pressure of 6.2 pounds. Nitrogen at a temperature of 3l6'.5 F. and a pressure of 5.4 pounds flows throughline 96 into heat exchanger 90 where it is warmed to a temperature of 303 F. in indirect heat exchange with the nitrogen reflux stream flowing through branch line 89. The nitrogen at a temperature of 303 F. iiows through exchanger 83 where it is warmed to a temperature of 293 F., at which temperature, as hereinabove described, it enters exchanger 19.

Oxygen at a temperature of 293 F. ancla pressure of 6.6 pounds flows through line.03, is warmed inits Iiowthrough exchanger '81 toa temperature of 287 F. by indirect heat exchange with a nitrogen stream owing through line 85. yThe oxygen-flows through line 94 into the base of column ll. From exchanger-.81 a portion ofthe nitrogenflows through 1ine88 to the top of column 16, the remainder of the nitrogen iiowing through branch line 89 and -through exchanger 96 where it is cooled to a temperature of 30l.2 F. The nitrogen at this temperature is flashed in its flow through valve 92; its temperature is thereby reduced to 3l6.5 F. and its pressure to 5.4 pounds, at which temperature and pressure it enters the top of column l1.

Upon reversal vwhich may take place everythree minutes, the air passes through the paths in 'exchangersll and 39 through which the nitrogen and oxygen passed during the preceding step of .the process and the nitrogen and oxygen pass throughvthe. paths in .exchangers lwand `39 through which the air passed during the preceding step of the process. The ilow of the various streams is otherwise substantially the same as hereinabove described and the temperature and pressure conditions remain the same. The nitrogen in its ilow through exchanger and the oxygen in its flow through exchanger 39 remove by sublimation and evaporation the carbon dioxide and frost, if any, deposited in the paths traversed by the air during the preceding step of the process. Thus, in the continual operation, upon each reversal the nitrogen and oxygen rectification products effect removal of the carbon dioxide and frost, if any, deposited in the paths through which the air has passed in the preceding step of the process.

The modification of Figure 2 diiers from that of Figure 1 chieiiy in that the reversing exchangers of Figure 2 `are of the regenerative type, not the recuperative type, as in Figure l, and oxygen is recycled through the cold end of the regenerators to obtain temperature conditions therein facilitating purging. The rectication system of Figure 2 is substantially the same as that of Figure 1 and like parts are indicated by the same reference characters.

In Figure 2, a regenerator assembly is shown involving two regenerator pairs and |06. Regenerator pair |05 consists of regenerators |01, |08, which may be and preferably are of the type disclosed and claimed in co-pending application Serial No. 783,498, led November 1, 1947, now Patent No. 2,585,912, although any other suitable type of regenerator may be used, if desired. As shown in Figure 2, the upper regenerator |01 comprises a housing |09 having a top port H0, base port |H and having a plurality of packing units H2 therein. Each packing unit desrably consists of a tubular support H3 on which is mounted a stack H4 of thin plate-like polygonal members of high heat conducitng material, desirably aluminum or copper, each having in the face thereof a multiplicity of closely spaced passages formed by cutting the plate-like members along closely spaced lines and deilecting the material between each such pair of lines to provide vanes defining these passages. One end of the tubular support H3 leads into a header H5 and the other end into a second header H6. For a more complete description of the construction of such packing units reference may be had to the aforesaid co-pending application.

Regenerator |08 structurally is substantially the same as |01. Regenerator pair |06 consists of regenerators H1 and H8, each structurally substantially the same as regenerator |01. Regenerators |01 and |08 and H1 and H8 have the ports H0 and H| interconnected for flow from one regenerator to another, as shown in Figure 2.

Header IB of regenerator |01 is connected with header I5 of regenerator |08 by a main H9. A main connects header H6 of regenerator H1 with header H5 of regenerator H8. The two mains H9 and |20 are connected by a main |2|.

The top headers H5 of regenerators |01 and H1 are connected by a main |22. The bottom headers H6 of regenerators |08 and H8 are interconnected by a main |23. In the apparatus of Figure 2, streams of nitrogen rectification product and air iiow alternately over the packing units disposed within the regenerator pairs |05, |06, the nitrogen imparting its cold content to the packing members and the air recovering this cold when it flows thereover during the Succeeding step of the process. Oxygen rectification 12 product flows through main |22, headers H5, tubes I3, giving up its cold content to the packing members, which cold content is recovered by the air passing over the packing members. The oxygen leaves regenerators |08, H8 through main |23.

A portion of the oxygen flowing through mains H9, |20 is withdrawn through lines |2I, |24 by blower |25 and is passed through a damper chamber |26 of the same type as damper chamber 2| of Figure l, which minimizes fluctuations in the temperature of the oxygen stream thus withdrawn. This oxygen stream from damper charnber |26 passes through a line |21 leading into a non-reversing exchanger |28 through which passes a minor portion of the air stream flowing through a line |29 into expander 1|. The minor portion of the air stream is thus heated to a predetermined constant temperature at which temperature it enters expander 1|. From exchanger |28 the warmed oxygen stream flows through a line |30 into an exchanger |3| through which flows the nitrogen stream passing through line |32, the nitrogen stream thus being warmed by the oxygen stream flowing through exchanger |3I. From exchanger |3| the oxygen stream enters oxygen line 59 Where it mixes with the oxygen stream flowing from the low pressure column 11, the resultant mixed oxygen stream entering main |22 communicating with the top headers H5 in the regenerators |01 and H1.

As above indicated, the recirculated oxygen passing through exchanger |28 warms the minor portion of the air stream flowing through line |29 to a temperature such that when introduced into the expander 1| liquefaction of air within this expander does not take place. From the expander 1| the expanded air is supplied to the low pressure stage 11 of the rectication system through line 12. In exchanger |3| the recirculated oxygen flows in indirect heat exchange relation with the nitrogen which flows from the rectification system through line |32. Thus the nitrogen enters the regenerator pair |05 or |06 at a higher temperature than would otherwise be the case. This nitrogen flows through one of the regenerator pairs |05, |06 and removes therefrom carbon dioxide and other condensibles deposited therein by aii` during the preceding step of the process. The eiliciency of the purging action of the nitrogen is materially improved by its entering the regenerator pairs |05, |05 at such higher temperature yas hereinabove described, since the preheating of the nitrogen in this manner results in temperature conditions within the regenerator optimum for the removal of the carbon dioxide.

Reversal of flow of nitrogen and air through regenerator pairs |05, |05 is accomplished by a pair of reversing valves |33, |34. Reversing valve |33 is provided with an air inlet |35, a pair of lines |36, |31 leading to ports IH of the regenerators |08, H8 and a nitrogen exit line |38. The other reversing valve |34. is provided with a pair of lines |39, |40 leading to the ports H0 of regenerators |01, H1, nitrogen line |32 and an air exit line IM. This air exit line communicates with the damper chamber |42 corresponding to damper chamber E0 of Figure 1 and of the same construction. From damper chamber |42 a line 8| leads to non-reversing exchanger 80, as in the modication of Figure 1. Air line 8| is provided with the branch line |29 through which, as hereinabove described, a minor portion of the cooled air flows from line 8| through exchanger |28 to expander 1|,

aezisgaosf.

lin` the operation of 'the Iapparatus of'fFigure v2,11 airrat` a pressurefof 60' to ilipounds and a/temg.A perature of from .'102to.110`F."issupplied through line I35'fandpas indicated bythe full line .valve settings; `iovvs through Valve I33,1ine.| 31 into and I through regenerators II8,'I I1 `where itf's cooledto.=fa ltemperature close toi'its liquefaction point 1 at the pressure prevailing .in these .regenerators;

The thus cooled air-exits. through 'line IllIiintoy valve IM from 'whichthe air flows vthroughf'line IML and-damper chamber I42J Amajor portion ofV thegair leaving this chamber at a substantially constant temperature flows through line 8l thence through line 13 'andexchanger 'I9 into the rectica-tion columnv l5.'- portion of the cooledair -fiows through line IZB; heat exchanger IZB to expander 1I.

2 to 12 pounds passes to the '10W pressure stage 'VI ofthe recticationsystem. Simultaneously,

nitrogenfiiowsthrough line I32,`Valve I34,f line` 139,'regenerators IGI; IDS'gi-vingup its cold lto the packing units in these 'regenerators valves-i353 and'nitrogenexit line i355.V

Oxygen from the vrectification system flows through line 59,` exchanger 8G, main I22,`headers f Ii5,=tubes v i3 within the regenerators IM, III;

headers yI i5 'and connecting mains II9,' HIL` A portion of this oxygen is withdrawnas product through main 523 -after its newv through theheadersandftubes vin the regenerators HI8; I I8.

Thel remainder is recirculated by blowerA IE5 through damper'chamber i255, which minimizes iiuctuaticns in lthe temperature of ther oxygen stream that isfrecirculated. From damper cham'.-

beri255 the oxygen stream passes into exchanger s I2@ where it serves to warmthe minor..airrstream flowing lto the i expander I I. From: this nonrever-sing exchanger 428 the. recirculating oxygen stream :flows through line I 3i) into phon-reversing exchanger iliwhereiit '.servestto Warm-the ni.- trogen f stream flowingfthroughf line x I 32. this nonwreversing exchanger, I3! the recirculated oxygen stream4 enters line ,59 :at'axtemeperature substantially" the ysaine i the tempera-A ture oivthe oxygen flowing through this 1ine, the

resultant oxygen stream-.being passed-'through the headersi I5, Mia and 4connectingtuhes,I I3 in/the'; regenerator Ypairs It; Miti, apart orv the oxygen `seing withdrawn throughxnain IRI and line IZA-f by pump :IE5: fand the rest withdrawn as product irom..main I 23,?as Al'iereinaloove described.`

Uponv reversal, which may takenplace l every three minutes, as `indicated hy the dotteduline,y valve settings, air :flows through valve 1I3%,;line;

i393, regenerators l, mi and is refrigerated close to its liquefaction point in itsiiow through these regenerators The'air exits through line.A

I3@ vandfows through valve E34 :into :line IM,A andthence through these-me flow pathsas hereinabove described.

generators iii, IIS; exiting: through. line I3'l, valve ISS and nitrogen exitline I38. Oxygen iiowsthrough the. same. .paths asduring the.-

precedingistep .of .the processVnamely, vthrough the tubesin vtl'ieregenerator pairs. II15,. IU5 coe currentlyA with the ,stream of nitrogen-flowing through regenerators IH, IIB and countercurrent v`to `the Ystream ,of 'Lairowing 4through the regenerators Iii'i,L IIiBin. indirect heat exchange'` relation therewith... The, nitrogen `Whichi al` ternately flows through' one or the other of the into the non-reversing exchanger 80,' and?.

The remaining minor'` Fiornthis expander the expanded air at a pressure of from The thusy warmedy nitrogen exits through line -IiiyV From.'-

Simultaneously nitrogen.` flows Ythrough lineivalve ISIL. line I'lIIl,f.re-

regeneratorrv rpairs ,il 05', .I 06 .removestherefromf carbon dioxide and :otherlfcondensiblzes deposited therein :from the :air during Ythe precedinglstep of ith-el .processn..

It'is preferred to effect 'removal of` ymoisture and carhondioxide=both -in the" reversing exchange-rsf tY will be Lunderstood,"however,-that, .if desired',ithefmoisture may heremovedfrom-r the air L1py-any conventional means and'dry air Y containing -carhonidioxide passedthrough the exchangers, 'as' hereinabove disclosed. Inftherevent dryiair `isl'supplied to the A4equipment of lF'ig-urey l,` reversing ValVeSHZQjJIiS-"may advantageously be moved'to a position between exchanger sections ff I I; I2y anddihdl so that the reversal of the 'air and nitrogen streams and ofthe air and oxygen streams occursonly'insections I2 'and 4|,Wheref in the carbon" dioxide is` deposited-by the` air stream: Operation of such equipment is preferahlycarried out so that the temperature -at the-- warm end oiexch'anger'sections vI2 and 4I is -at least, slightly,higher ,than` the temperature at- Whiohcarbon dioxide begins to deposit from the strearns. In generaLLthe Warm endof these rexchangers Yshould be at a temperature-aloove` about 180i F.

The `expressionsreversing ,the flow ,of air yand nitrogen??r andfreversal are usedherein inthe sensecoinmonly employedin this art, namely, to

mean the. switching,of,.theilow of, two streams, for`r example, `the air.- and Athe nitrogen or oxygen iows lthrough the p-athithrough WhichJhadpre-l viouslyriiowedi fthe-nitrogen1 or oxygen andV the nitrogen'-zor oxygen fiowsthrough -thepath through' which i had :previously flowed the fair.

Sinceicertain changes; maybe madein carrying -`out the above f processes Without,l departingA `from `the scopefof the invention, it is intended 'f that all matter containedin the above descriptionA shall lbe interpreted'as illustrativefand 'not in a limiting sense.

What is claimed is:

1. An improvementn the process of producinggoxygen. by the liquefaction'and rectification of i air involving flovv` of air under pressure through' a reversing exchanger in indirect heat exchange relation with ,a rectication product, periodicallyreversing theflow of air and rectification product through their respective paths of iiow inlsaidreversingexchanger, passing a portion of the thus cooledair ythrough at least the coldk end of.said reversing, exchanger to warm said air and produce ,temperature conditions Within said reversing Y exchanger to facilitate purging thereof by the rectification product passing therethrough, and expanding the warmed air to produce refrigeration in amount` adequate to compensate for enthalpy loss and heat leaks into ,the system, which improvement vcomprises passingvthe warmed airf'owing from said reversing exchangerthrougha unidirectional path of; flow; containing a substantially isothermal* mass of Vhighheatconducting material to V'minimize fluctuations in the temperature of said warmed air prior to expanding same.

2. An improvement in the process of produc-A ing oxygen by the liquefaction and rectification of air in low and high pressure stages involving flowing air under pressure through a reversing exchanger to recover the cold content of a rectification product, dividing the air into two streams, one consisting of a minor portion of the air and the other a major portion, expanding the minor stream thereby supplying to the process refrigeration in amount adequate to compensate for enthalpy loss and for heat leaks into the system, introducing the expanded air into the low pressure stage of the rectification system, introducing the major portion of the stream of air into the high pressure stage of the rectification system, rectifying the air to produce said rectification product, passing the rectification product through said reversing exchanger to impart its cold content to the incoming air stream, and periodically reversing the flow of air and rectification product through their respective paths in said reversing exchanger, the improvement which comprises passing said minor portion of the air stream through a unidirectional path of flowA over a substantially isothermal mass of high heat conducting material prior to expanding same to minimize fluctuations in the temperature of the air stream subjected to expansion.

3. The process of producing oxygen by the liquefaction and rectification of air in low and high pressure stages involving flowing air under pressure through a reversing exchanger to recover the cold content of a rectification product, passing the air stream leaving said reversing exchanger through a unidirectional path of flow over a substantially isothermal mass of high heat conducting material to minimize fluctuations in the temperature of said air stream, dividing the resulting air stream into minor `and major portions, dividing the minor portion into two parts, passing one of said parts in indirect heat exchange relation with the air and rectification product to warm said part of the air stream, thereafter passing the thus warmed part of the air stream in a unidirectional path of flow over a substantially isothermal mass of high heat conducting material to minimize fluctuations in the temperature of this air stream, mixing the resulting air stream with th second part of the minor portion to produce a mixed air stream at a temperature such that on expansion no liquefied air is formed in the expander, expanding the resulting air stream, introducing the expanded air into the low pressure stage of the rectification system, introducing the major portion of the stream of air into the high pressure stage of the rectification system, rectifying the air to produce said rectification product, passing the rectification product through said reversing exchanger to impart its cold content to the incoming air stream, and periodically reversing the flow of air and rectification product through their respective paths in said reversing exchanger,

4. A process of producing oxygen which comprises flowing two streams of air through paths in a pair of heat exchange zones, in one of said zones flowing a stream of nitrogen rectification product in indirect heat exchange relation with one of said air streams and in the other of said zones flowing a stream of oxygen rectification product in indirect heat exchange relation with the other of said air streams, periodically reversing the flow of air and oxygen and of air and nitrogen through their respective paths in said zones, mixing the air streams leaving both of said zones into a common stream, passing the thus mixed air stream through a unidirectional path of flow over a substantially isothermal mass of high heat conducting material to minimize fluctuations in the temperature of the resulting air stream, introducing the resulting air stream at a substantially constant temperature into the rectification system, rectifying the air to produce said oxygen and nitrogen products of rectification, and passing the said oxygen and nitrogen rectification products through their flow paths in the said zones.

5. A process of producing oxygen which comprises flowing two streams of air through paths in a first and second heat exchange zone, in the iirst zone flowing a stream of nitrogen rectification product in indirect heat exchange relation with one of said air streams and in the other of said zones flowing a stream of oxygen rectification product in indirect heat exchange relation with the other of said air streams, periodically reversing the flow of air and oxygen and of air and nitrogen through their respective paths in said zones, mixing the air streams leaving both of said zones into a common stream, passing the thus mixed air stream through a unidirectional path of flow over a substantially isothermal mass of high heat conducting material to minimize fluctuations in the temperature of the resulting air stream, dividing the air stream into major and minor portions, introducing the major portion of the air into a high pressure stage of a rectification system comprising high and low pressure stages, recirculating the minor portion of the air through the first-mentioned zone in indirect heat exchange relation with the air and nitrogen passing therethrough thus warming the recirculated air stream, passing the warmed air stream in a unidirectional path of flow over a substantially isothermal mass of high heat conducting material to minimize fluctuations in the temperature of the warmed air stream, expanding the resulting warmed air stream, introducing the expanded air into the low pressure stage of the rectification system, rectifying the air to produce said oxygen and nitrogen products of rectification, and passing the said oxygen and nitrogen rectification products through their paths in the said zones.

6. A process of producing oxygen by the liquefaction and rectification of air, which comprises flowing air under pressure through a heat exchange zone through which also flows a rectification product to recover the cold content of said rectification product, recirculating through said heat exchange zone a second rectification product in indirect heat exchange relation with the air and the first-mentioned rectification product passing therethrough thus warming the second-mentioned rectification product, passingthe thus warmed second rectification product through a unidirectional path containing a substantially isothermal mass of high heat conducting material to minimize fluctuations in the temperature of said second stream of rectication product, passing the said second stream of rectification product in indirect heat exchange relation with the first-mentioned rectification product flowing to said heat exchange zone to Warm said first-mentioned rectification product, and periodically reversing the flow of air and 1'? the rst-mentioned rectiiication product through said heat exchange zone.

7. A process as defined in claim 6, in which the first-mentioned rectification product is nitrogen, the second-mentioned rectification product is oxygen, and the air stream leaving said heat exchange zone is passed in a unidirectional path over a substantially isothermal mass of high heat conducting material prior to introduction into a rectification system to minimize fluctuations in the temperature of the air stream entering said rectication system.

8. In an apparatus for the liquefaction and rectiiication of mixed gases involving: a heat exchanger having a first flow path and a second flow path in indirect heat exchange with each other to eiect transfer of heat from a feed stream of said mixed gases to a stream of gaseous rectification product thereof flowing, respectively, through said rst flow path and said second ow path; reversing means at each end of said heat exchanger for periodically flowing said feed stream through said second flow path and said rectification product stream through said first flow path; a third flow path in said heat exchanger in indirect heat exchange With at least one of said rst and second flow paths to warm a gaseous stream derived from said feed stream after iiowing through said heat exchanger, each of the aforesaid three flow paths containing a mass of high heat conducting material; the im provement which comprises a thermally isolated damper chamber containing a mass of high heat conducting material and having an inlet and an outlet, and a conduit connecting said inlet directly and solely to the discharge end of said third iioW path.

9. Apparatus as dened in claim 8, in which the outlet of said chamber is connected to the inlet of an expander.

10. Apparatus as dened in claim 8, in which said chamber contains a mass of high heat conducting material of from 1% to 10% by Weight of the Weight of such material in the third iloW 0 Number path in said heat exchanger, with which said chamber communicates.

11. In the liquefaction and rectification of air involving: now of air under pressure through a lirst ow path whereinsaid air is cooled to a temperature near its liquefaction point to condense and deposit out carbon dioxide; W of a cold rectification product of said air through a second flow path wherein said rectification product is warmed and sublimes a carbon dioxide deposit from said second now path; periodic reversal of the flow of said air and said rectification product through said second flow path and said iirst now path, respectively; and now of a cold stream derived from said cooled air through a third flow path in indirect heat exchange with at least one of said rst and second 110W paths to warm said stream and to facilitate the sublimation of carbon dioxide; the improvement which comprises passing said stream, after flowing through said third flow path and while still substantially at the temperature at which said stream discharges from said third flow path, through a unidirectional flow path containing a substantially isothermal mass of high heat conducting material to minimize iiuctuations in the temperature of said stream.

l2. The process of claim 11 wherein said stream owing through said third ow path is nitrogen rectification product.

13. The process of claim 11 wherein said stream, after passing through said unidirectional flow path, is expanded with the performance of work to provide refrigeration to said process.

JOHIN A. I-lUFNAGEL.

References Cited in the le 0f this patent UNITED STATES PATENTS Name Date Borchardt et al. June 29, 1937 Trumpler Feb. 8, 1949 Crawford Feb. 7, 1950 Roberts Dec. 19, 1950 

